Electron discharge device for ultra high frequencies



Oct. 12, 1948. P. T. SMITH ET AL ELECTRON DISCHARGE DEVICE FOR ULTRA HIGH FREQUENCIES 3 Sheets-Sheet l Filed March 18, 1943 Bnvenfot PHILIP T. .SMITH 8f HOWARD R. HEGBQR Get. i2, E948. P. T. SMITH ETAI. 2,451,249

ELECTRON DISCHARGE DEVICE FOR ULTRA HIGH FREQUENCIES Filed March 18, 1943 3 Sheets-Sheet 2 Enventor @HMP i'. 5mn-rs1 g( WARD R. HEGBQR Cet. l2, 1948. P. T. SMITH ET Al.

ELECTRON DISCHARGE DEVICE FOR ULTRA HIGH FREQUENGIES 5 Sheets-Sheet 5 Filed March 18, 1945 .lnnentor PHILIP-l, SMITH Gttorneg Patented er. 12, 1948 UNITED PAT-@TENT ICE i ELEcTRoN DISCHARGE DEVICE non ULTRA f 1HIGHFREQUENCIES Philia T.' smith and Howard R; Hegbarmrince- "ton,"N. J.`,' ass'g'rs to Radio Corpration"of Amrica, a Y'coi-11ieration of Delaware Application Marchas, 1943`,- serial No. '479,550

L17 cleans.

l Our invention relates to electron'discharge-devices and associated circuitslusefulat ultra high frequencies, more particularly to `Vsuch devices utilizing closed resonant circuits or resonators.

` A still further 'object of'bur invention is'to provide'such a leading anglein'such a'. devicewithout A'using external transmission" lines.

The novel features Whi'cli'we believe tobe vchar- At the higher frequencies, the physical dimen-y 5 a'cteristic of our inventionare'setforth With "parsions of tuned circuits are small. '.Ihus -When ticularity in the appended claim-s; but the inventubes arel to be used in conjunction with these tion' itself will bestbe" understood'by reference circuits the tube elements become an appreciable to the following descriptiontaken' in connection physical part of the circuit. In present ultra high withthe accompanying drawing in'whcliFigure 1 frequency technique of closed resonant circuits is alongtudinal Section o'fone formg of an 'electron or resonators, which provide particularly suitable discharge device and circuit 'made "according to circuits at ultra high frequencies, are'Y directly our invention,"Fi'gure 2 is a transversesection coupled to the electrodes of an electron discharge taken along the'line 2-2 o'flfig'ur'e I showing' dedevice. In Aone form of device such as the sotails of the grid coi'i'structionjli'igure? is a modicalled grounded grid triode, use is made of two l5 ication ofV the `structure'""shown"in` Figure 2, closed resonant circuits or resonators. Oneof Figure 4 is'an equivalentcircuit diagraniAo'fA-the these resonators is coupled-between the cathode device shown' in'"Figure 1," Figure 5 is) a longiand the grid and the' other is coupled between tu'dinaI section' of a modification ofu an electron the grid and the collector orV anode-'radio fredischarge device made"accordingl to'our invention, quency energy being extracted from the-closed 20 andligur'e 6 is a"schematic) longitudinal section resonant circuit between the grid and anode by of thetube strl'ctur'e andassociated circuits. means of a coupling loop. `In'one form ofsuch "An electron di'schargedeviceand associated tube the gridV structure almost completely' -eleccircuit made'ac'cording to our invention is's'liyvn trically isolates the interior of one resonator from in Figure 1. The. cathode includes l -cupls'haped the other. element' i0 heated' byiheater fl'la'nd coated," in a For microwaves at ultra` high frequencies; the manner tobedescriloedfwith emitting 'materialY l2. time required for an'electron: to traverse'anfy prac- A grid l 4 of a construction to'-b`e''de''s'crlgedv and tical cathode-grid distance becomes-an apprehaving-the same cross sectional configuration is4 ciable fraction of the 'Wave period resulting; in positioned between the indirectly heated cathode. undesirable losses both in the. :input and output IB and the collector or'anode I3, provided with a circuits. As a consequence for the efficient operconcave surface so that the surfaces of the ation or these tubes and particularly as an oscilcathode, grid and anode. nest Within eachv other.` lator it becomes necessary to compensate'for'this lThe cathode-grid resonatorwhich may be used transit time. A partialcompensation:-forftransit as an input'resonator and coupled betWeen`-the time losses may be obtained if the radio frequency cathode and the grid comprises the inner cupvoltage of the grid-cathode resonator operates shaped memberV I5 and the outer cupshaped at a leading anglev with respect toithefradio fremember i6 having a bottom element l'l which cluency voltage of the grid-collectorv resonator. closes one end of the tubeand provides a support This can be done by feeding back-'energy from for the member i5., which -is secured byscrews. i8 the plate resonator to the cathode resonatorl in 40 extendingthrough the flange on memberY l5.finto the proper phase by employing complicated eX- the element H. Thefmember L5-supports atits. termal transmis-sion lines, inner -end the circular lolocl;y 19on :-which-the It is an object of our inventiontoobtairr-an cathodev IU is secured by theeollar I-Sand screws electron discharge device andcircuitparticularly i9', amica ring 20- electrically'insulating-the. useful at ultra high frequencies. cathode from the inner tubular membervlf The A. further object of our invention is to provide cathode is provided with-a hollow tubular cathode such an electron discharge device' and-circuit lead 2l provided with the tubular ange 23-and which willv compensate for lelectron transit time sealed to the element |27 by means of the-glass. eiiects. tubular member 22.- This cathode-lead ZL-a'lso More specifically it is an object of/our invention 50 actslas the outer conductor of -acooling Asystem to provide a leading angle betweenthe radio provided'Withlan*innertubular-member Mythe frequency voltage in the gridl-cathodefresonator cooling'medium'passing linto'the'interior of-the and the radio frequency voltage in the 1gricleplate cathode throughone of lthe-tubular members and resonator of apparatus utilizinganfelectron-'dises outwardlythroughthe-other -tubularniembee in charge device and resonators. a manner well known, The tubular-memberand and the grid includes the outer tubular member i 3E! coaxial with and surrounding the inner tubular member '31, their ends being closed by transverse element 32 integral with the outer tubular member 3l?, the two members being secured to- Y gether by means of screw elements 33. The anode or collector i3 is insulatingly supported onthe inner element 3l by means of the insulating'dis'cs or mica collars 3d, a screw member 31 securing the collector to the inner tubular member 3| by means of the clamping disc 35 and insulating collar member 36. Thus while the collector is a part of the resonator circuit it is insulated from it to permit a diierent D. C. potential to be applied to the collector through either of the two leads 38 or 4G provided with the sealing member 39 sealed to the element 32 by means of the tubular insulating member 32. The members 38 and Il@ may be used to introduce a cooling medium to the interior of the collector I3.

The grid I4, closing the ends of the resonators connected between the cathode and the grid and between the grid and the anode, is supported by the flange element i6 to which it is secured by screws, the two portions of the device being clamped together by means of the screw member d5 extending through the iiange IB' and into the 'flange 30 on the outer tubular member 30 of the grid-anodeY resonator. A gasket 46 may be provided between the two flanges. If desired continuous pumping can be used to maintain a vacuum within 'the device by connecting tube 4l to a pump, but the structure may be sealed off from'the pump. A coupling loop 64 to permit coupling of the energy from the anode-grid'resonator coupled between the grid and the collector is positioned within the reentrant seal 43. l

In order to assure desirable and most efhcient operation of the device shown in Figure 1, the electrons received by the collector or anode should reach the anode at such time that the radio frel quency voltage on thev anode is a minimum. In this way maximum energy is delivered to the anode circuit with the least dissipation of energy in the form of heat, which reduces the eiciency of the apparatus. At the lower frequencies the Voltage on the grid is 180 out of phase with the voltage on the anode, and electrons from the cathode move between the'cathode and the collector inthe period of time which is extremely shortrin comparison with the Yperiod of the applied voltage to the grid, so that the electrons reach the anode at the proper time, or when the anode radio frequency voltage is a minimum. At the higher frequencies however, the transmit time of the electrons between the cathode and anode or Vcollector forms an appreciable part of the period of the applied voltage so that the electrons reach the anode or collector at a time when the voltage is not a minimum or not 180 out of phase with the gridz voltage. Thus the electrons are collected by the anode at a time when the voltage on'the anode is greater than the desirable voltage causing more of the energy to be lost in the form of heat. It wou-ld, therefore, be desirable to'haveV the electrons leave the cathode at such time that is a minim they willreach the anode when the 1*-7-1 potential V u Stated another way, at the lower frequencies it is desirable to have the cathode r-f voltage swing in phase with the anode r-f voltage, since the electrons from the cathode move between the cathode and collector in a period of time which is small in comparison with theY period of the applied r-'f voltage. At the higher frequencies,

however, the transit time of the Aelectrons between the cathode and anode or collector forms an appreciable part ofthe period of the applied r-vf voltage so that under the above conditions the Aelectrons reach the anode or collector after y the voltage has reached a minimum, so that the electrons are collected by the anode at a time when the voltage on the anode is greater than the desirable voltage causing more energy to be lost in the form of heat. We partially compensate for this eliect by providing a leading angle between the cathode-grid 1-;f Voltage with respect to the anode-grid r-f voltage. A leading Vangle is attained if a resistive component is added K to the capacitive reac'tancey of Ythe VYcathode-grid resonator; The energy losses-in the cathodegrid resonator, dueto loading by conduction currents and heating from circulating currents provide this resistive component. This angle can be further changed or partially controlled by taking out at least part of the output energy from the cathode-grid resonator.

In other words, the input resonator must display a capacitive reactance. In a device utilizing a coaxial'line resonant cavity or resonator, the

length of the line should be so chosen thatit is substantially a one-quarter or a three-quarter or tures 5|'.

tween the grid wires 52'.-

any odd multiple of a quarter wavelength long. This will cause the input circuit or the gridcathode circuit to display a capacitive reactance.V

Thus the electrons can be made to reach the anode when the r-f voltage is at a minimum.

In order to provide the necessary feedback be-V tween the two resonators so that the device may function as an oscillator without the use of an external transmission line,` we provide a grid of novel construction. I As shown in Figure 2 the grid I4 is provided with a large central aperture 50 and with a plurality oi smaller apertures surrounding this aperture 50. At the periphery of the grid we provide a plurality of kapertures of llargersize than the'apertures 52 for a purpose to be described. In'the form shown in Figure 3 the grid I4 is provided with transverse wires 52. extending across the grid and with the outer aper- The purpose ofthe central aperture 50 is to increase the capacityV coupling betweenrcathode and anode to such an extent that the desired feedback will occur within the tube.' The purpose of the smaller apertures 52 is to obtain the necessary controlof the electrons passing between the cathode and grid so that the grid will retain its normal control. The apertures 5| provide an electromagnetic couplingk between the fields vwithin the two' resonators. In order to preventV emission betwen`the grid and cathode at the point where ionly capacity coupling is desired, that is'through the aperture 50, the portion of the cathode surface registering with this aper' ture is vnot coated and to reduce the-grid current which might otherwise occur, the cathode Vis coated only on those Aportions of its surface registering with the apertures 52. v

In the form of gridshown in Figure 3 the cathode'surface is coated only on those .portions iof' the cathode surface registeringwith the space be- Y An equivalent circuit diagram of our device is shown in Figure e'. The elements K, G and P represent the cathode, grid and plate. The elemen-'ts L1 and C1 connected between grid and cathode represent the distributed capacity and inductance of the input resonator comprising elements i5, I6 and H, while the resistance Ri represents the resistance of the resonator circuit andthe resistance due to the grid loading between the grid and the cathode.

'I'he capacity C2 and induotance L2 represent the distributed inductance and capacity of the output resonator comprising elements 38, 32 and 3l and the resistance R2 is that of the circuit and the resistance between plate and grid when current flows. The capacity C represents that capacity existing between the cathode and anode due to the aperture 5i? at the center of the grid, the symbol I4 representing the electromagnetic coupling through the openings 5i existing between the two elds within the resonators.' According to our theory aperture 59 provides the return circuit for the radio frequency currents. Thus the electrons leaving the cathode at a leading angle with respect to the r-f voltage within the resonator pass through the grid into the resonator coupled between the anode and the grid and arrive at the anode at the proper time.

Part of the energy from the anode-grid resonator is fed back into the cathode-grid resonator by means of the capacity between the anode and cathode, through the apertures 5S and 5.2. The aperture 53 makes it possible to adjust this capacity. The circuit is completed through the aperture 5i. In other words, the capacity through the apertures and 52 is represented by C553 in Figure 4 whereas the apertures 5I complete the circuit at I@ in Figure e.

Figure 6 is a schematic longitudinal section of. an electron discharge device made according to our invention and the connections between the various elements and the source .of voltages necessary for the operation of the device. A cathode heating voltage is applied by means of the heating transformer 55 and 4bias on the grid with respect to cathode obtained by biasing resistor 56 through which the cathode is connected to ground, grid l. being connected to ground at 58. Collector voltage is shown at 59.

While we have shown in Figure l an arrangement in which the electrodes extend transversely of the coaxial line resonators, in Figure 5 we show a modification in which the cathode and grid and anode merge into the longitudinal vsurface of the concentric lines. As shown in Figure 5 .the cathode G is provided with a heater l, the cathode 503 serving as an extension of the internal coaxial member S6. The cathode Si! is .supported on member v by means of the insulated screw members 66" clamping the cathode to the inner tubular member 6E' but insulated therefrom by means of the insulator or mica separator 65. Surrounding the cathode is a grid B3 provided with longitudinally extending wiresforming an extension of the outer tubular lmember 58 and having cap 62 provided with aperture 54. The members E5 and 68 provide an input resonator connected between the cathode and grid, the cathode again being coated only on the portions registering with the apertures between the grid wires and not being coated at its end in registry with the apertures 64 and cap B2. The output resonator connected between the grid and collector is formed by means of the cup-shaped member E5 serving as the collector and the outer tubular member 69 insulatingly connected to member 55 by means of the separator 69 which may be of mica and screws 69", the coaxial member 68 and 69 providing the outer resonator. The cathode heater leads "61 extend through tubular sealing member 5l sealed to the inner tubular member 66 and collector lead-in 12 lextends through tubular member V'13 which is sealed to the outer 4casing I9 which may be evacuated and sealed off at 74. A reentrant seal 'H may be provided to permit the insertion of a coupling loop within the output resonator to extract energy from the eld within this resonator.

As in the other forms, the capacity coupling is provided through aperture S4 and the elds Within the resonators are coupled Vby means of the apertures 68 `formed in the outer tubular member 68 of the cathode-grid resonator. The device otherwise functions in a manner similar to that shown in Figure 1.

A device Vof the kind described operated satisfa'ctorily at about 600 megacycles with reasonable eiliciency. Tests also indicated that the tube functioned in the manner described above.

While we have indicated the preferred embodiments of our invention of which we are now awa-re and have also indicated only one specinc application -for which our invention may be ernployed, it will be apparent that our invention is -by no means limited to the exact forms illustrated vor the use indicated, but that many variations may be made in the particular structure used and `the purpose for which it is employed without departing .from the scope of our invention as set forth in the appended claims.

What we claim as new is:

l. An electron discharge device having a cathode and an oppositely disposed anode, a yconductpartition positioned between said cathode and said anode and including a grid, a resonator coupled between said partition and cathode, and a second resonator coupled between said partition and anode, said cathode having emitting and substantially non-emitting areas, the grid portion of said partition being provided with apertures registering with said emitting areas and said partition having another aperture providing a passageway between said resonators for providing electromagnetic coupling, said grid having another aperture toprovide anode-cathode capacity feedback coupling, said last aperture registering with a non-emitting portion of said cathode.

2. An electron discharge device having a cathode and an oppositely disposed anode, a 4resonator coupled to said cathode, and a second resonator coupled to said anode, said resonators having a common conducting partition between them, said partition providing a grid positioned between said cathode and said anode, said cathode having emitting and substantially non-emitting areas, said partition being provided with an apertured portion registering with an emitting area on said cathode surface, and said partition having an apertured portion providing a passageway between the interior of said resonators for providing electromagnetic coupling, said grid having another aperture to provide anode-cathode capacity feedback coupling, said last aperture registering with a non-emitting portion of said cathode.

3. An electron discharge device having a cathode and an oppositely disposed anode, a con-ducting partition positioned between said cathode and said anode and including a grid portion, a

resonator coupled between said partition and cathode and enclosing said cathode, and a second resonator coupled between said` grid and anode and enclosing said anode, said cathode having emitting and substantially non-emitting areas, the grid portion of said partition being provided with apertures registering with said emitting areas, and said partition having other apertures providing passageways between the interior of said resonators for providing electromagnetic coupling, said grid having another aperture to provide anode-cathode capacity feedback coupling, said last aperture registering with anonemitting portion of said cathode.

4. An electron discharge device havinga cathode and an oppositely disposed anode, a grid positioned between said cathode and anode, a resonator coupled between said grid and cathode and enclosing said cathode, and a second resonator coupled between said grid and anode and enclosing said anode, said resonators being oppositely disposed, said grid providing a partition between said resonators, said cathode having a substantially flat surface with emitting and substantially non-emitting areas, said grid being provided with an aperture registering with an emitting area and at least one other aperture registering with a non-emitting area of said cathode.

5. An electron dischargedevice having a cathode and an oppositely disposed anode, a grid positioned between said cathode and anode, a resonator coupled between said grid and cathode and enclosing said cathode, and a second resonator coupled between said grid and anode and enclosing said anode, said resonators being oppositely disposed, said grid providing a partition between said resonators, said cathode having `a substantially fiat surface with emitting and substantially non-emitting areas, said grid being provided with apertures registering with emitting areas of said cathode, and a plurality of other apertures at least one of which registers with a non-emitting area of said cathode.

6. An electron discharge device having a cathode and an oppositely disposed anode, a grid positioned between said cathode and anode, a resonator coupled between said grid and cathode and enclosing said cathode, and a second resonator coupled between said grid and anode and enclosing said anode, said resonators being oppositely disposed, said grid providing a partition between said resonators, said cathode having emitting and substantially non-emitting areas, said grid comprising a plate-like structure provided with an enlarged aperture at its center and a plurality of smaller apertures, said cathode being provided on its surface with emitting areas registering only with the smaller apertures.

7. An electron discharge device having a cathode and an oppositely disposed anode,`a grid'positioned between said cathode and anode, a resonat-or coupled between said grid and cathode and enclosing said cathode, and a second resonator coupled between said grid and anode and enclosing said anode, said resonators being oppositely disposed, said grid providing a partition between said resonators, said cathode having a substantially flat surface with emitting and substantially non-emitting areas, said grid being lprovided with apertures registering with the emitting areas and having a plurality ofapertures positioned' near its periphery and providing passageways betweenthe interiors of the resonators.

8% 8. An electron discharge device having a cathode and an oppositely disposed anode, a grid positioned between said cathodeand anode, a

resonator coupled between said rgrid and cathode and enclosing said cathode, and a second resonator coupled between said grid and anode and enclosing saidanode, said resonators being oppositely disposed, said grid providing a par-r tition between said resonators, said cathode ,hav-

ing emitting and substantially non-emitting areas, said grid Icomprising a plate-like structure vprovided with an enlarged aperture at its center and a plurality of smaller apertures surrounding said enlarged aperture, said cathode being provided with emitting areas only on its surface registering with the smaller apertures, said grid Ahaving a plurality of apertures positioned near its outer periphery, said last plurality of apertures providing passageways betweenv the interiors of the resonators.

9. An electron discharge ldevice having a cathode and an oppositely disposedY anode, ak grid positioned between said cathode and anode, a resonator coupled between said gridY and cathode and enclosing said cathode, and a second res-vk onator coupled between said grid and anode and enclosing said anode, said resonators being oppositely disposed, said grid providing a partition between said resonators, said grid having a centrally positioned enlarged aperture, a plurality of smaller apertures surrounding said enlarged.V

aperture, a plurality of otherrapertures npositioned near the outer periphery of said grid member, said cathode being coated with emitting material only on its surface registering with the plurality of smaller apertures.

10. An electron discharge device having a plate-like cathode, a plate-likeanodaand a grid positioned betweensaid cathode and anodea.

concentric line resonator closed at one end and having an inner conductor and a tubular member K surrounding said inner conductor, said cathode being insulatingly supported on said inner conductor remote from the onator, said grid extending across and 'closing the end of said resonator adjacent said cathode, a second concentric line kresonator having one end closed and including an inner conductor surrounded by an outer tubular member, said anodeY being insulatingly supported on the inner conductor at the end of said second concentric line resonator remote from its closed end, the endrof said second resonator adjacent said anode also being closed by said grid, said grid providing a partition .between said resonators. f

11.V An electron discharge device having a plate-like cathode, an oppositely disposed platelike anode, and a grid positioned between said cathode and anode, a concentric line resonator closed at one end and having an inner conductor and a tubular member surrounding said inner conductor, said cathode being insulatingly supported on said inner-conductor remote from the closed end of said resonator, said grid extending on the inner conductor at the end of said secondY concentric line resonator remote from is closed end, the end of said second resonator adjacent said anode also being closed by said grid, said- Y grid providing a partitionV between said resonators, said grid'r'having a plurality of aperturesclosed end of said vresnear its periphery providing passageways between the interiors of said coaxial line resonators.

12. An electron discharge device having a plate-like cathode, an oppositely disposed platelike anode, and a grid positioned between said cathode and anode, a concentric line resonator closed at one end and having an inner conductor and a tubular member surrounding said inner conductor, said cathode being insulatingly supported on said inner conductor remote from the closed end of said resonator, said grid extending across and closing the end of said resonator adjacent said cathode, a second concentric line rescnator having one end closed and including an inner conductor surrounded by an outer tubular member, said anode being insulatingly supported on the inner conductor at the end of said second concentric line resonator remote from its closed end, the end of said second resonator adjacent said anode also being closed by said grid, said grid providing a partition between said resonators, said grid being provided with an enlarged centrally positioned aperture and having a plurality of smaller apertures surrounding said centrally positioned aperture and a plurality of apertures near its periphery providing passageways between the interiors of said coaxial line resonators, said cathode having areas coated with emitting material and non-coated areas, said coated areas registering with the plurality of smaller apertures.

13. An electron discharge device having a cathode surrounded by a cup-shaped grid and a cup-shaped anode, a iirst tubular member supporting said cathode and a second tubular member surrounding said rst tubular member and supporting said grid and providing with said first tubular member a iirst resonator coupled between the cathode and grid and a third tubular member surrounding said first and second Y tubular members, and supporting said cupshaped anode and providing with said second tubular member a second resonator, said grid having an enlarged aperture in its cup-shaped f end, the second tubular member supporting said grid having other apertures providing passageways between the interiors of said resonators.

14. An electron discharge device having a tubular indirectly heated cathode surrounded by a cup-shaped grid and a cup-shaped anode, a nrst tubular member insulatingly supporting' said cathode and a second tubular member surrounding said rst tubular member and supporting said grid and providing with said first tubular member a first resonator coupled between the cathode and grid and a third tubular member surroundingf said i'irst and second tubular members, and connected to but insulatingly supporting said cup-shaped anode and providing with said second tubular member a second resonator, said grid comprising a cap having an enlarged aperture in said cap and a plurality of longitudinally extending rod-like elements connected to said cap, said cathode being coated with emitting material only over its surface areas registering with the space between said rod like elements, said second tubular member having apertures providing passageways between the interior of said resonators.

15. An electron discharge device having a cathode, and an anode, and a grid positioned between said cathode and anode, a concentric line resonator connected between said cathode and grid, said grid extending across and closing the end of said resonator adjacent said cathode, a second concentric line resonator connected between said anode and said grid, the end of said second resonator adjacentl said anode being closed by said grid, said grid providing a partition between said resonators, said cathode having emitting and substantially non-emitting areas, said grid being provided with a plurality of apertures registering with the emitting areas of said cathode and having an apertured portion between the interiors of said concentric line resonators, the coaxial line resonator connected between said cathode and grid being a quarter wavelength long of the operating frequency oi said electron discharge device.

16. An electron discharge device having a cathode and an anode, and a grid positioned between said cathode and anode, a concentric line resonator connected between said cathode and grid, said grid extending across and closing the end of said resonator adjacent said cathode, a second concentric line resonator connected between said anode and said grid, the end of said second resonator adjacent said anode being closed by said grid, said grid providing a partition between the interior of said resonators, said cathode having emitting and substantially non-emitting areas, said grid being provided with a plurality of apertures registering with the emitting areas of said cathode, and having an apertured portion between the interiors of said coaxial line resonators, the coaxial line resonators connected between said cathode and grid being of the order of an odd multiple of quarter wavelengths long of the operating frequency of said electron discharge device.

17. An electron discharge device having a cathode surrounded by a cup-shaped grid and a cup-shaped anode, a first tubular member connected to said cathode and a second tubular member surrounding said first tubular member and connected to said grid and providing with said first tubular member a rst resonator coupled between the cathode and grid, and a third tubular member surrounding said rst and second tubular members and connected to said cupshaped anode and providing with said second tubular member a second resonator, the second tubular member connected to said grid having an aperture providing a passageway between the interiors of said resonators.

PHILIP T. SMITH. HOWARD R. I-IEGBAR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED S-TATES PATENTS 

